Plasma processing method and plasma processing apparatus

ABSTRACT

A decrease of an etching rate of a substrate can be suppressed, and energy of ions irradiated to an inner wall of a chamber main body can be reduced. A plasma processing apparatus includes a DC power supply configured to generate a negative DC voltage to be applied to a lower electrode of a stage. In a plasma processing performed by using the plasma processing apparatus, a radio frequency power is supplied to generate plasma by exciting a gas within a chamber. Further, the negative DC voltage from the DC power supply is periodically applied to the lower electrode to attract ions in the plasma onto the substrate placed on the stage. A ratio occupied, within each of cycles, by a period during which the DC voltage is applied to the lower electrode is set to be equal to or less than 40%.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Japanese Patent Application No.2017-157832 filed on Aug. 18, 2017, the entire disclosures of which areincorporated herein by reference.

TECHNICAL FIELD

The various aspects and embodiments described herein pertain generallyto a plasma processing method and a plasma processing apparatus.

BACKGROUND

In the manufacture of an electronic device, a plasma processingapparatus is used. The plasma processing apparatus is generally equippedwith a chamber main body, a stage and a radio frequency power supply. Aninternal space of the chamber main body is configured as a chamber. Thechamber main body is grounded. The stage is provided within the chamberand configured to support a substrate placed thereon. The stage includesa lower electrode. The radio frequency power supply is configured tosupply a radio frequency power to excite a gas within the chamber. Inthis plasma processing apparatus, ions are accelerated by a potentialdifference between a potential of the lower electrode and a potential ofthe plasma, and the accelerated ions are irradiated to the substrate.

In the plasma processing apparatus, a potential difference is alsogenerated between the chamber main body and the plasma. When thepotential difference between the chamber main body and the plasma islarge, energy of ions irradiated to an inner wall of the chamber mainbody is increased, so that particles are released from the chamber mainbody. The particles released from the chamber main body contaminates thesubstrate placed on the stage. To suppress the generation of theseparticles, Patent Document 1 discloses a technique using an adjustmentmechanism configured to adjust a ground capacity of the chamber. Theadjustment mechanism described in Patent Document 1 is configured toadjust an area ratio between a cathode and an anode facing the chamber,that is, an A/C ratio.

Patent Document 1: Japanese Patent Laid-open Publication No. 2011-228694

SUMMARY

As one kind of the plasma processing apparatus, there is used a plasmaprocessing apparatus configured to supply a radio frequency power forbias (“radio frequency bias power”) to the lower electrode. The radiofrequency bias power is supplied to the lower electrode to increase anetching rate of the substrate by increasing the energy of the ionsirradiated to the substrate. In this plasma processing apparatus, if thepotential of the plasma is increased, the potential difference betweenthe plasma and the chamber main body is increased, and the energy of theions irradiated to the inner wall of the chamber main body is alsoincreased. In this regard, it is required to suppress a decrease of theetching rate of the substrate and reduce the energy of the ionsirradiated to the inner wall of the chamber main body.

In one exemplary embodiment, there is provided a plasma processingmethod performed in a plasma processing apparatus. The plasma processingapparatus includes a chamber main body, a stage, a radio frequency powersupply and one or more DC power supplies. An internal space of thechamber main body is configured as a chamber. The stage is providedwithin the chamber main body. The stage includes a lower electrode. Thestage is configured to support a substrate placed thereon. The radiofrequency power supply is configured to supply a radio frequency powerfor exciting a gas supplied into the chamber. The one or more DC powersupplies are configured to generate a negative DC voltage to be appliedto the lower electrode. The plasma processing method includes (i)supplying the radio frequency power from the radio frequency powersupply to generate plasma of the gas supplied into the chamber; and (ii)applying the negative DC voltage to the lower electrode from the one ormore DC power supplies to attract ions in the plasma onto the substrate.In the applying of the DC voltage, the DC voltage is applied to thelower electrode periodically, and a ratio occupied, within each ofcycles, by a period during which the DC voltage is applied to the lowerelectrode is set to be equal to or less than 40%.

Dependency of an etching rate of the substrate upon the ratio occupied,within each cycle, by the period during which the negative DC voltage isapplied to the lower electrode, that is, a duty ratio is small.Meanwhile, when the duty ratio is small, particularly, when the dutyratio is equal to or less than 40%, an etching rate of the chamber mainbody is greatly decreased. That is, energy of ions irradiated to aninner wall of the chamber main body is decreased. Thus, according to theplasma processing method of the present exemplary embodiment, a decreaseof the etching rate of the substrate can be suppressed, and the energyof the ions irradiated to the inner wall of the chamber main body can bereduced.

The ratio, that is, the duty ratio is set to be equal to or less than35%. According to the present exemplary embodiment, the energy of theions irradiated to the inner wall of the chamber main body can befurther reduced.

The plasma processing apparatus includes multiple DC power supplies asthe one or more DC power supplies. The DC voltage applied to the lowerelectrode within each of the cycles is generated by DC voltagesoutputted from the multiple DC power supplies in sequence. According tothe present exemplary embodiment, a load of each of the multiple DCpower supplies is reduced.

In the plasma processing method according to the present exemplaryembodiment, the radio frequency power is supplied in the period duringwhich the DC voltage is applied, and the supplying of the radiofrequency power is stopped in a period during which the applying of theDC voltage is stopped. In the plasma processing method, the supply ofthe radio frequency power may be stopped in the period during which theDC voltage is applied, and the radio frequency power is supplied in aperiod during which the application of the DC voltage is stopped.

In another exemplary embodiment, there is provided a plasma processingapparatus. The plasma processing apparatus includes a chamber main body,a stage, a radio frequency power supply, one or more DC power supplies,a switching unit and a controller. An internal space of the chamber mainbody is configured as a chamber. The stage is provided within thechamber main body. The stage includes a lower electrode. The stage isconfigured to support a substrate placed thereon. The radio frequencypower supply is configured to supply a radio frequency power forexciting a gas supplied into the chamber. The one or more DC powersupplies are configured to generate a negative DC voltage to be appliedto the lower electrode. The switching unit is configured to allow theapplication of the DC voltage to the lower electrode to be stopped. Thecontroller is configured to control the switching unit. The controllercontrols the switching unit such that the negative DC voltage from theone or more DC power supplies is applied to the lower electrodeperiodically to attract ions in plasma of a gas generated within thechamber onto the substrate, and such that a ratio occupied, within eachof cycles, by a period during which the DC voltage is applied to thelower electrode is set to be equal to or less than 40%.

The controller may control the switching unit such that the ratio, thatis, the duty ratio is set to be equal to or less than 35%.

The plasma processing apparatus further includes multiple DC powersupplies as the one or more DC power supplies. The controller controlsthe switching unit such that the DC voltage applied to the lowerelectrode within each of the cycles is generated by DC voltagesoutputted from the multiple DC power supplies in sequence.

The controller controls the radio frequency power supply such that theradio frequency power is supplied in the period during which the DCvoltage is applied, and the supply of the radio frequency power isstopped in a period during which the application of the DC voltage isstopped. The controller may control the radio frequency power supplysuch that the supply of the radio frequency power is stopped in theperiod during which the DC voltage is applied, and the radio frequencypower is supplied in a period during which the application of the DCvoltage is stopped.

As described above, it is possible to suppress the decrease of theetching rate of the substrate and reduce the energy of the ionsirradiated to the inner wall of the chamber main body.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the detailed description that follows, embodiments are described asillustrations only since various changes and modifications will becomeapparent to those skilled in the art from the following detaileddescription. The use of the same reference numbers in different figuresindicates similar or identical items.

FIG. 1 is a diagram schematically illustrating a plasma processingapparatus according to an exemplary embodiment;

FIG. 2 is a diagram illustrating a power supply system and a controlsystem of the plasma processing apparatus shown in FIG. 1;

FIG. 3 is a diagram illustrating a circuit configuration of a DC powersupply, a switching unit, a radio frequency filter and a matching deviceshown in FIG. 2;

FIG. 4 is a timing chart for a plasma processing method according to anexemplary embodiment performed by using the plasma processing apparatusshown in FIG. 1;

FIG. 5A and FIG. 5B are timing charts showing a plasma potential;

FIG. 6A and FIG. 6B are timing charts for a plasma processing methodaccording to another exemplary embodiment;

FIG. 7 is a diagram illustrating a power supply system and a controlsystem of a plasma processing apparatus according to yet anotherexemplary embodiment;

FIG. 8 is a diagram illustrating a power supply system and a controlsystem of a plasma processing apparatus according to still yet anotherexemplary embodiment;

FIG. 9 is a timing chart for the plasma processing method according toan exemplary embodiment performed by using the plasma processingapparatus shown in FIG. 8;

FIG. 10 is a diagram illustrating a power supply system and a controlsystem of a plasma processing apparatus according to still yet anotherexemplary embodiment;

FIG. 11 is a circuit diagram illustrating an example of a waveformadjuster;

FIG. 12A is a graph showing a relationship between a duty ratio and anetching amount of a silicon oxide film of a sample, which is attached toa surface of a ceiling plate 34 at a chamber 12 c side, obtained in afirst test experiment, and FIG. 12B is a graph showing a relationshipbetween the duty ratio and an etching amount of a silicon oxide film ofa sample attached, which is to a sidewall of the chamber main body 12,obtained in the first test experiment;

FIG. 13 is a graph showing a relationship between the duty ratio and anetching amount of a silicon oxide film of a sample, which is placed onan electrostatic chuck 20, obtained in the first test experiment; and

FIG. 14A is a graph showing etching amounts of silicon oxide films ofsamples, which are attached to the surface of the ceiling plate 34 atthe chamber 12 c side respectively, obtained in a second test experimentand a comparative experiment, and FIG. 14B is a graph showing etchingamounts of silicon oxide films of samples, which are attached to thesidewall of the chamber main body 12 respectively, obtained in thesecond test experiment and the comparative experiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part of the description. In thedrawings, similar symbols typically identify similar components, unlesscontext dictates otherwise. Furthermore, unless otherwise noted, thedescription of each successive drawing may reference features from oneor more of the previous drawings to provide clearer context and a moresubstantive explanation of the current exemplary embodiment. Still, theexemplary embodiments described in the detailed description, drawings,and claims are not meant to be limiting. Other embodiments may beutilized, and other changes may be made, without departing from thespirit or scope of the subject matter presented herein. It will bereadily understood that the aspects of the present disclosure, asgenerally described herein and illustrated in the drawings, may bearranged, substituted, combined, separated, and designed in a widevariety of different configurations, all of which are explicitlycontemplated herein.

Hereinafter, various exemplary embodiments will be described in detailwith reference to the accompanying drawings. In the various drawings,same or corresponding parts will be assigned same reference numerals.

FIG. 1 is a diagram schematically illustrating a plasma processingapparatus according to an exemplary embodiment. FIG. 2 is a diagramillustrating a power supply system and a control system of the plasmaprocessing apparatus shown in FIG. 1. A plasma processing apparatus 10shown in FIG. 1 is configured as a capacitively coupled plasmaprocessing apparatus.

The plasma processing apparatus 10 is equipped with a chamber main body12. The chamber main body 12 has a substantially cylindrical shape. Aninternal space of the chamber main body 12 is configured as a chamber 12c. The chamber main body 12 is made of, by way of example, but notlimited to, aluminum. The chamber main body 12 is connected to theground potential. A plasma-resistant film is formed on an inner wallsurface of the chamber main body 12, that is, on a wall surfaceconfining the chamber 12 c. This film may be a film formed by anodicoxidation or a film made of ceramic such as yttrium oxide. Further, apassage 12 p is formed at a sidewall of the chamber main body 12. When asubstrate W is carried into the chamber 12 c or carried out of thechamber 12 c, the substrate W passes through this passage 12 p. A gatevalve 12 g is provided along the sidewall of the chamber main body 12 toopen/close this passage 12 p.

Within the chamber 12 c, a supporting member 15 is upwardly extendedfrom a bottom of the chamber main body 12. The supporting member 15 hasa substantially cylindrical shape and is made of an insulating materialsuch as ceramic. A stage 16 is mounted on the supporting member 15. Thestage 16 is supported by the supporting member 15. The stage 16 isconfigured to support the substrate W within the chamber 12 c. The stage16 includes a lower electrode 18 and an electrostatic chuck 20. In theexemplary embodiment, the stage 16 further includes an electrode plate21. The electrode plate 21 is made of a conductive material such asaluminum and has a substantially disk shape. The lower electrode 18 isprovided on the electrode plate 21. The lower electrode 18 is made of aconductive material such as, but not limited to, aluminum and has asubstantially disk shape. The lower electrode 18 is electricallyconnected with the electrode plate 21.

A path 18 f is formed within the lower electrode 18. The path 18 f is apassage for a heat exchange medium. A liquid coolant or a coolant (forexample, Freon) which cools the lower electrode 18 by being vaporized isused as the heat exchange medium. The heat exchange medium is suppliedvia a pipeline 23 a into the path 18 f from a chiller unit provide at anoutside of the chamber main body 12. The heat exchange medium suppliedinto the path 18 f is returned back into the chiller unit via a pipeline23 b. That is, the heat exchange medium is supplied into the path 18 fto be circulated between the path 18 f and the chiller unit.

The electrostatic chuck 20 is provided on the lower electrode 18. Theelectrostatic chuck 20 has a main body made of an insulator and afilm-shaped electrode provided within the main body. The electrode ofthe electrostatic chuck 20 is electrically connected with a DC powersupply. If a voltage is applied to the electrode of the electrostaticchuck 20 from the DC power supply, an electrostatic attractive force isgenerated between the electrostatic chuck 20 and the substrate W placedthereon. The substrate W is attracted to and held by the electrostaticchuck 20 by the generated electrostatic attractive force. A focus ringFR is provided on a peripheral portion of the electrostatic chuck 20.The focus ring FR has a substantially annular plate shape and is madeof, by way of non-limiting example, silicon. The focus ring FR isprovided to surround an edge of the substrate W.

The plasma processing apparatus 10 is equipped with a gas supply line25. Through the gas supply line 25, a heat transfer gas, for example, aHe gas from a gas supply mechanism is supplied into a gap between a topsurface of the electrostatic chuck 20 and a rear surface (bottomsurface) of the substrate W.

A cylindrical member 28 is extended upwards from the bottom of thechamber main body 12. The cylindrical member 28 is extended along anouter circumferential surface of the supporting member 15. Thecylindrical member 28 is made of a conductive material and has asubstantially cylindrical shape. The cylindrical member 28 is connectedto the ground potential. An insulating member 29 is provided on thecylindrical member 28. The insulating member 29 has insulation propertyand is made of, by way of non-limiting example, quartz or ceramic. Theinsulating member 29 is extended along an outer circumferential surfaceof the stage 16.

The plasma processing apparatus 10 is further equipped with an upperelectrode 30. The upper electrode 30 is disposed above the stage 16. Theupper electrode 30 closes a top opening of the chamber main body 12along with a member 32. The member 32 has insulation property. The upperelectrode 30 is supported at an upper portion of the chamber main body12 with the member 32 therebetween. If a first radio frequency powersupply 61 to be described later is electrically connected to the lowerelectrode 18, this upper electrode 30 is connected to the groundpotential.

The upper electrode 30 includes a ceiling plate 34 and a supporting body36. A bottom surface of the ceiling plate 34 forms and confines thechamber 12 c. The ceiling plate 34 is provided with a multiple number ofgas discharge holes 34 a. Each of these gas discharge holes 34 a isformed through the ceiling plate 34 in a plate thickness directionthereof (vertical direction). This ceiling plate 34 may be made of, byway of example, but not limitation, silicon. Alternatively, the ceilingplate 34 may have a structure in which a plasma-resistant film is formedon a surface of a base member made of aluminum. This film may be oneformed by anodic oxidation or one made of ceramic such as yttrium oxide.

The supporting body 36 is configured to support the ceiling plate 34 ina detachable manner, and is made of a conductive material such as, butnot limited to, aluminum. A gas diffusion space 36 a is formed withinthe supporting body 36. A multiple number of gas holes 36 b are extendeddownwards from the gas diffusion space 36 a to communicate with the gasdischarge holes 34 a, respectively. Further, the supporting body 36 isprovided with a gas inlet port 36 c through which a gas is introducedinto the gas diffusion space 36 a, and a gas supply line 38 is connectedto this gas inlet port 36 c.

The gas supply line 38 is connected to a gas source group 40 via a valvegroup 42 and a flow rate controller group 44. The gas source group 40includes a plurality of gas sources. The valve group 42 includes aplurality of valves, and the flow rate controller group 44 includes aplurality of flow rate controllers. Each of the flow rate controllersbelonging to the flow rate controller group 44 may be implemented by amass flow controller or a pressure control type flow rate controller.Each of the gas sources belonging the gas source group 40 is connectedto the gas supply line 38 via a corresponding valve belonging to thevalve group 42 and a corresponding flow rate controller belonging to theflow rate controller group 44. The plasma processing apparatus 10 iscapable of supplying gases from one or more gas sources selected fromthe plurality of gas sources belonging to the gas source group 40 intothe chamber 12 c at individually controlled flow rates.

A baffle plate 48 is provided between the cylindrical member 28 and thesidewall of the chamber main body 12. By way of non-limiting example,the baffle plate 48 may be made of an aluminum base member coated withceramic such as yttrium oxide. This baffle plate 48 is provided with amultiple number of through holes. Under the baffle plate 48, a gasexhaust pipe 52 is connected to the bottom of the chamber main body 12.The gas exhaust pipe 52 is connected to a gas exhaust device 50. The gasexhaust device 50 has a pressure controller such as an automaticpressure control valve and a vacuum pump such as a turbo molecular pump,and is configured to decompress the chamber 12 c.

As depicted in FIG. 1 and FIG. 2, the plasma processing apparatus 10 isfurther equipped with the first radio frequency power supply 61. Thefirst radio frequency power supply 61 is configured to generate a firstradio frequency power for plasma generation by exciting a gas within thechamber 12 c. The first radio frequency power has a frequency rangingfrom 27 MHz to 100 MHz, for example, 60 MHz. The first radio frequencypower supply 61 is connected to the lower electrode 18 via a firstmatching circuit 65 of a matching device 64 and the electrode plate 21.The first matching circuit 65 is configured to match an output impedanceof the first radio frequency power supply 61 and an impedance at a loadside (lower electrode 18 side). Further, the first radio frequency powersupply 61 may not be electrically connected to the lower electrode 18but be connected to the upper electrode 30 via the first matchingcircuit 65.

The plasma processing apparatus 10 is further equipped with a secondradio frequency power supply 62. The second radio frequency power supply62 is configured to generate a second radio frequency power for ionattraction into the substrate W. A frequency of the second radiofrequency power is lower than the frequency of the first radio frequencypower and falls within a range from 400 kHz to 13.56 MHz, for example,400 kHz. The second radio frequency power supply 62 is connected to thelower electrode 18 via a second matching circuit 66 of the matchingdevice 64 and the electrode plate 21. The second matching circuit 66 isconfigured to match an output impedance of the second radio frequencypower supply 62 and the impedance at the load side (lower electrode 18side).

The plasma processing apparatus 10 is further equipped with a DC powersupply 70 and a switching unit 72. The DC power supply 70 is configuredto generate a negative DC voltage. The negative DC voltage is applied asa bias voltage for attracting ions into the substrate W placed on thestage 16. The DC power supply 70 is connected to the switching unit 72.The switching unit 72 is electrically connected with the lower electrode18 via a radio frequency filter 74. In the plasma processing apparatus10, one of the DC voltage generated by the DC power supply 70 and thesecond radio frequency power generated by the second radio frequencypower supply 62 is selectively supplied to the lower electrode 18.

The plasma processing apparatus 10 is further equipped with a controllerPC. The controller PC is configured to control the switching unit 72.The controller PC may be further configured to control either one orboth of the first and second radio frequency power supplies 61 and 62.

In the exemplary embodiment, the plasma processing apparatus 10 mayfurther include a main control unit MC. The main control unit MC isimplemented by a computer including a processor, a storage device, aninput device, a display device, and so forth, and controls individualcomponents of the plasma processing apparatus 10. To elaborate, the maincontrol unit MC executes a control program stored in the storage deviceand controls the individual components of the plasma processingapparatus 10 based on recipe data stored in the storage device. Underthis control, the plasma processing apparatus 10 performs a processdesignated by the recipe data.

Now, reference is made of FIG. 2 and FIG. 3. FIG. 3 is a diagramillustrating a circuit configuration of the DC power supply, theswitching unit, the radio frequency filter and the matching device. TheDC power supply 70 is a variable DC power supply and is configured togenerate a negative DC voltage to be applied to the lower electrode 18.

The switching unit 72 is configured to stop the application of the DCvoltage to the lower electrode 18 from the DC power supply 70. In theexemplary embodiment, the switching unit 72 includes field effecttransistors (a FET 72 a and a FET 72 b), a capacitor 72 c and a resistorelement 72 d. The FET 72 a may be, by way of example, a N-channelMOSFET. The FET 72 b may be, by way of example, a P-channel MOSFET. Asource of the FET 72 a is connected to a cathode of the DC power supply70. One end of the capacitor 72 c is connected to the cathode of the DCpower supply 70 and the source of the FET 72 a. The other end of thecapacitor 72 c is connected to a source of the FET 72 b. The source ofthe FET 72 b is connected to the ground. A gate of the FET 72 a and agate of the FET 72 b are connected to each other. A pulse control signalfrom the controller PC is supplied to a node NA connected between thegate of the FET 72 a and the gate of the FET 72 b. A drain of the FET 72a is connected to a drain of the FET 72 b. A node NB connected to thedrain of the FET 72 a and the drain of the FET 72 b is connected to theradio frequency filter 74 via the resistor element 72 d.

The radio frequency filter 74 is a filter configured to reduce or blocka radio frequency power. According to the exemplary embodiment, theradio frequency filter 74 has an inductor 74 a and a capacitor 74 b. Oneend of the inductor 74 a is connected to the resistor element 72 d. Theone end of the inductor 74 a is connected with one end of the capacitor74 b. The other end of the capacitor 74 b is connected to the ground.The other end of the inductor 74 a is connected to the matching device64.

The matching device 64 is equipped with the first matching circuit 65and the second matching circuit 66. In the exemplary embodiment, thefirst matching circuit 65 has a variable capacitor 65 a and a variablecapacitor 65 b, and the second matching circuit 66 has a variablecapacitor 66 a and a variable capacitor 66 b. One end of the variablecapacitor 65 a is connected to the other end of the inductor 74 a. Theother end of the variable capacitor 65 a is connected to the first radiofrequency power supply 61 and one end of the variable capacitor 65 b.The other end of the variable capacitor 65 b is connected to the ground.One end of the variable capacitor 66 a is connected to the other end ofthe inductor 74 a. The other end of the variable capacitor 66 a isconnected to the second radio frequency power supply 62 and one end ofthe variable capacitor 66 b. The other end of the variable capacitor 66b is connected to the ground. The one end of the variable capacitor 65 aand the one end of the variable capacitor 66 a are connected to aterminal 64 a of the matching device 64. The terminal 64 a of thematching device 64 is connected to the lower electrode 18 via theelectrode plate 21.

Now, a control by the main control unit MC and the controller PC will beexplained. In the following description, reference is made to FIG. 2 andFIG. 4. FIG. 4 is a timing chart for a plasma processing methodaccording to an exemplary embodiment performed by using the plasmaprocessing apparatus shown in FIG. 1. In FIG. 4, a horizontal axisrepresents time, and a vertical axis indicates a power of the firstradio frequency power, the DC voltage applied to the lower electrode 18from the DC power supply 70, and the control signal outputted by thecontroller PC. In FIG. 4, a high level of the power of the first radiofrequency power implies that the first radio frequency power is beingsupplied to generate plasma, and a low level of the first radiofrequency power means that the supply of the first radio frequency poweris stopped. Further, in FIG. 4, a low level of the DC voltage impliesthat the negative DC voltage is applied to the lower electrode 18 fromthe DC power supply 70, and 0 V of the DC voltage implies that the DCvoltage is not applied to the lower electrode 18 from the DC powersupply 70.

The main control unit MC designates the power and the frequency of thefirst radio frequency power to the first radio frequency power supply61. In the present exemplary embodiment, the main control unit MCdesignates, to the first radio frequency power supply 61, a timing forstarting the supply of the first radio frequency power and a timing forstopping the supply of the first radio frequency power. In a periodduring which the first radio frequency power is supplied by the firstradio frequency power supply 61, the plasma of the gas within thechamber is generated. That is, in this period, there is performed aprocess S1 of supplying the radio frequency power from the radiofrequency power supply to generate the plasma. Further, in the exampleof FIG. 4, the first radio frequency power is continuously suppliedwhile the plasma processing method of the exemplary embodiment is beingperformed.

The main control unit MC designates, to the controller PC, a frequencywhich defines a cycle in which the negative DC voltage from the DC powersupply 70 is applied to the lower electrode 18 and a duty ratio. Theduty ratio is a percentage occupied, within a single cycle (PDC in FIG.4), by a period (T1 in FIG. 4) during which the negative DC voltage fromthe DC power supply 70 is applied to the lower electrode 18. This dutyratio is set to be equal to or less than 40%. In the present exemplaryembodiment, this duty ratio is set to be equal to or less than 35%.

The controller PC generates a control signal according to the frequencyand the duty ratio designated by the main control unit MC. The controlsignal generated by the controller PC may be a pulse signal. As anexample, as depicted in FIG. 4, the control signal generated by thecontroller PC has a high level in the period T1 and a low level in theperiod P2. The period T2 is a period except the period T1 within thesingle cycle PDC. Alternatively, the control signal generated by thecontroller PC may have a low level in the period T1 and a high level inthe period T2.

According to the present exemplary embodiment, the control signalgenerated by the controller PC is applied to the node NA of theswitching unit 72. If the control signal is received, in the period T1,the switching unit 72 connects the DC power supply 70 and the node NB,thus allowing the negative DC voltage from the DC power supply 70 to beapplied to the lower electrode 18. Meanwhile, in the period T2, theswitching unit 72 disconnects the DC power supply 70 and the node NBfrom each other to allow the negative DC voltage from the DC powersupply 70 not to be applied to the lower electrode 18. Accordingly, asshown in FIG. 4, the negative DC voltage from the DC power supply 70 isapplied to the lower electrode 18 in the period T1, whereas theapplication of the negative DC voltage from the DC power supply 70 tothe lower electrode 18 is stopped in the period T2. That is, in theplasma processing method according to the exemplary embodiment, there isperformed a process S2 of applying the negative DC voltage from the DCpower supply 70 to the lower electrode 18 periodically.

Here, reference is made to FIG. 5A and FIG. 5B. FIG. 5A and FIG. 5B aretiming charts showing a plasma potential. In the period T1, since thenegative DC voltage from the DC power supply 70 is applied to the lowerelectrode 18, positive ions in the plasma are moved toward the substrateW. Accordingly, as shown in FIG. 5A and FIG. 5B, the plasma potential isdecreased in the period T1. Meanwhile, in the period T2, since theapplication of the negative DC voltage from the DC power supply 70 tothe lower electrode 18 is stopped, movement of the positive ions isreduced, and electrons in the plasma move mainly. Accordingly, theplasma potential is increased in the period T2.

In the timing chart of FIG. 5A, the duty ratio is reduced as compared tothe timing chart of FIG. 5B. If all conditions for generating the plasmaare same, neither a total amount of the positive ions nor a total amountof the electrons in the plasma depends on the duty ratio. That is, aratio between an area A1 and an area A2 in FIG. 5A is equal to a ratiobetween an area A1 and an area A2 in FIG. 5B. Therefore, if the dutyratio is small, a plasma potential PV in the period T2 is small.

Dependency of an etching rate of the substrate W upon the duty ratio,that is, the ratio occupied, within each cycle PDC, by the period T1during which the negative DC voltage is applied to the lower electrode18 is small. Meanwhile, if the duty ratio is small, particularly, whenthe duty ratio is equal to or less than 40%, the plasma potential isdecreased, so that the etching rate of the chamber main body 12 isgreatly reduced. Accordingly, by setting the aforementioned duty ratiofor the periodic application of the negative DC voltage to the lowerelectrode 18 to be equal to or less than 40%, the decrease of theetching rate of the substrate W can be suppressed, and the energy of theions irradiated to the inner wall of the chamber main body 12 can bedecreased. As a consequence, generation of particles from the chambermain body 12 is suppressed. Further, if the duty ratio is equal to orless than 35%, the energy of the ions irradiated to the inner wall ofthe chamber main body 12 can be further decreased

Now, other exemplary embodiments will be explained. FIG. 6A and FIG. 6Bare timing charts for a plasma processing method according to otherexemplary embodiments. In each of FIG. 6A and FIG. 6B, a horizontal axisindicates a time, and a vertical axis indicates a power of the firstradio frequency power and a DC voltage applied to the lower electrode 18from the DC power supply 70. In each of FIG. 6A and FIG. 6B, a highlevel of the power of the first radio frequency power indicates that thefirst radio frequency power is being supplied for plasma generation, anda low level of the power of the first radio frequency power indicatesthat the supply of the first radio frequency power is stopped. Further,in each of FIG. 6A and FIG. 6B, a low level of the DC voltage impliesthat the negative DC voltage is being applied to the lower electrode 18from the DC power supply 70, and 0 V of the DC voltage means that the DCvoltage is not applied to the lower electrode 18 from the DC powersupply 70.

In the exemplary embodiment shown in FIG. 6A, the negative DC voltagefrom the DC power supply 70 is periodically applied to the lowerelectrode 18, and the first radio frequency power is also suppliedthereto periodically for the plasma generation. In the exemplaryembodiment shown in FIG. 6A, the application of the negative DC voltagefrom the DC power supply 70 to the lower electrode 18 and the supply ofthe first radio frequency power are synchronized with each other. Thatis, the first radio frequency power is supplied in the period T1 duringwhich the DC voltage from the DC power supply 70 is applied to the lowerelectrode 18, and the supply of the first radio frequency power isstopped in the period T2 during which the application of the DC voltagefrom the DC power supply 70 to the lower electrode 18 is stopped.

In the exemplary embodiment shown in FIG. 6B, the negative DC voltagefrom the DC power supply 70 is periodically applied to the lowerelectrode 18, and the first radio frequency power is also suppliedthereto periodically for the plasma generation. In the exemplaryembodiment shown in FIG. 6B, a phase of the supply of the first radiofrequency power is reversed with respect to a phase of the applicationof the negative DC voltage from the DC power supply 70 to the lowerelectrode 18. That is, the supply of the first radio frequency power isstopped in the period T1 during which the DC voltage from the DC powersupply 70 is applied to the lower electrode 18, and the first radiofrequency power is supplied in the period T2 during which theapplication of the DC voltage from the DC power supply 70 to the lowerelectrode 18 is stopped.

In the exemplary embodiments shown in FIG. 6A and FIG. 6B, theaforementioned control signal from the controller PC is applied to thefirst radio frequency power supply 61. The first radio frequency powersupply 61 starts the supply of the first radio frequency power at atiming when the control signal from the controller PC rises (or falls)and stops the supply of the first radio frequency power at a timing whenthe control signal from the controller PC falls (or rises). In theexemplary embodiments shown in FIG. 6A and FIG. 6B, generation of anunexpected radio frequency power caused by intermodulation distortioncan be suppressed.

Now, plasma processing apparatuses according to several other exemplaryembodiments will be explained. FIG. 7 is a diagram illustrating a powersupply system and a control system of a plasma processing apparatusaccording to another exemplary embodiment. As shown in FIG. 7, a plasmaprocessing apparatus 10A according to the present exemplary embodimentis different from the plasma processing apparatus 10 in that the firstradio frequency power 61 includes the controller PC. That is, in theplasma processing apparatus 10A, the controller PC is configured as apart of the first radio frequency power supply 61. Meanwhile, in theplasma processing apparatus 10, the controller PC is configured as aseparate body from the first radio frequency power supply 61 and thesecond radio frequency power supply 62. Since, however, the controllerPC is a part of the first radio frequency power supply 61 in the plasmaprocessing apparatus 10A, the aforementioned control signal (pulsesignal) from the controller PC is not sent to the first radio frequencypower supply 61.

FIG. 8 is a diagram illustrating a power supply system and a controlsystem of a plasma processing apparatus according to yet anotherexemplary embodiment. A plasma processing apparatus 10B shown in FIG. 8is equipped with a plurality of DC power supplies 701 and 702 and aplurality of switching units 721 and 722. Each of the plurality of DCpower supplies 701 and 702 is the same as the DC power supply 70 andconfigured to generate a negative DC voltage to be applied to the lowerelectrode 18. Each of the plurality of switching units 721 and 722 hasthe same configuration as the switching unit 72. The DC power supply 701is connected to the switching unit 721. Like the switching unit 72, theswitching unit 721 is capable of stopping the application of the DCvoltage from the DC power supply 701 to the lower electrode 18. The DCpower supply 702 is connected to the switching unit 722. Like theswitching unit 72, the switching unit 722 is capable of stopping theapplication of the DC voltage from the DC power supply 702 to the lowerelectrode 18.

FIG. 9 depicts a timing chart for a plasma processing method accordingto the yet another exemplary embodiment performed by using the plasmaprocessing apparatus shown in FIG. 8. In FIG. 9, a horizontal axisrepresents a time, and a vertical axis indicates a summed DC voltage(that is, a DC voltage applied to the lower electrode 18), a DC voltageof the DC power supply 701 (that is, a DC voltage applied to the lowerelectrode from the DC power supply 701), and a DC voltage of the DCpower supply 702 (that is, a DC voltage applied to the lower electrodefrom the DC power supply 702). As illustrated in FIG. 9, in the plasmaprocessing apparatus 10B, a DC voltage applied to the lower electrode 18within each cycle PDC is generated by a plurality of DC voltagesoutputted from the plurality of DC power supplies 701 and 702 insequence. That is, in the plasma processing apparatus 10B, the DCvoltage applied to the lower electrode 18 within each cycle PDC isgenerated by a temporal sum of the plurality of DC voltages outputtedfrom the plurality of DC power supplies 701 and 702 in sequence.According to this plasma processing apparatus 10B, a load of each of theplurality of DC power supplies 701 and 702 is reduced.

In the plasma processing apparatus 10B, the controller PC outputs, tothe switching unit 721, a control signal having a high level (or a lowlevel) in a period during which the DC voltage from the DC power supply701 is applied to the lower electrode 18 and a low level (or a highlevel) in a period during which the DC voltage from the DC power supply701 is not applied to the lower electrode 18. Further, the controller PCoutputs, to the switching unit 722, a control signal having a high level(or a low level) in a period during which the DC voltage from the DCpower supply 702 is applied to the lower electrode 18 and a low level(or a high level) in a period during which the DC voltage from the DCpower supply 702 is not applied to the lower electrode 18. That is, thecontrols signals (pulse signals) having different phases arerespectively applied to the plurality of switching units connected tothe plurality of DC power supplies.

FIG. 10 is a diagram illustrating a power supply system and a controlsystem of a plasma processing apparatus according to still yet anotherexemplary embodiment. A plasma processing apparatus 10C shown in FIG. 10is different from the plasma processing apparatus 10 in that it isfurther equipped with a waveform adjuster 76. The waveform adjuster 76is connected between the switching unit 72 and the radio frequencyfilter 74. The waveform adjuster 76 is configured to adjust a waveformof the DC voltage outputted from the DC power supply 70 via theswitching unit 72, that is, the DC voltage having a negative value and avalue of 0 V alternately. To elaborate, the waveform adjuster 76 adjuststhe waveform of the DC voltage to be applied to the lower electrode 18such that the waveform of the corresponding DC voltage has a triangularshape. The waveform adjuster 76 is implemented by, by way ofnon-limiting example, an integration circuit.

FIG. 11 is a circuit diagram illustrating an example of the waveformadjuster 76. The waveform adjuster 76 shown in FIG. 11 is implemented byan integration circuit and has a resistor element 76 a and a capacitor76 b. One end of the resistor element 76 a is connected to a resistorelement 72 d of the switching unit 72, and the other end of the resistorelement 76 a is connected to the radio frequency filter 74. One end ofthe capacitor 76 b is connected to the other end of the resistor element76 a. The other end of the capacitor 76 b is connected to the ground. Inthe waveform adjuster 76 shown in FIG. 11, there is generated a delay inan increase and a decrease of the DC voltage outputted from theswitching unit 72 based on a time constant determined by a resistancevalue of the resistor element 76 a and an electrostatic capacitancevalue of the capacitor 76 b. Accordingly, according to the waveformadjuster 76 shown in FIG. 11, it is possible to apply a voltage having atriangular waveform to the lower electrode 18 intentionally. Accordingto the plasma processing apparatus 10C having this waveform adjuster 76,the energy of the ions irradiated to the inner wall of the chamber mainbody 12 can be adjusted.

So far, the various exemplary embodiments have been described. However,it should be noted that the above-described exemplary embodiments arenot anyway limiting, and various changes and modifications may be made.By way of example, the plasma processing apparatuses according to theabove-described various exemplary embodiments may not have the secondradio frequency power supply 62. That is, the plasma processingapparatuses according to the above-described various exemplaryembodiments may have a single radio frequency power supply.

Further, in the above-described various exemplary embodiments, theapplication of the negative DC voltage from the DC power supply to thelower electrode 18 and the stopping of this application are switched bythe switching unit. If, however, the DC power supply itself isconfigured to switch the output of the negative DC voltage and thestopping of the output of this negative DC voltage, the switching unitis not required.

Furthermore, the inventive configurations of the above-described variousexemplary embodiments may be combined in various ways. In addition,though the plasma processing apparatuses according to theabove-described exemplary embodiments are configured as capacitivelycoupled plasma processing apparatuses, a plasma processing apparatusaccording to a modified exemplary embodiment may be configured as aninductively coupled plasma processing apparatus.

Further, if the duty ratio is high, the energy of the ions irradiated tothe chamber main body 12 is increased. Accordingly, by setting the dutyratio to be of a high value, for example, larger than 40%, the cleaningof the inner wall of the chamber main body 12 can be performed.

Now, test experiments conducted regarding the plasma processing methodusing the plasma processing apparatus 10 will be discussed.

First Test Experiment

In the first test experiment, samples each having a silicon oxide filmare respectively attached to the surface of the ceiling plate 34 at thechamber 12 side and the sidewall of the chamber main body 12 and asample having a silicon oxide film is placed on the electrostatic chuck20 of the plasma processing apparatus 10. Then, plasma processing isperformed under the following conditions. Further, in the first testexperiment, the duty ratio of the negative DC voltage applied to thelower electrode 18 periodically is used as a variable parameter.

<Conditions for Plasma Processing in First Test Experiment>

-   -   Internal pressure of the chamber 12 c: 20 mTorr (2.66 Pa)    -   Flow rate of gases supplied into the chamber 12 c        -   C₄F₈ gas: 24 sccm        -   O₂ gas: 16 sccm        -   Ar gas: 150 sccm    -   First radio frequency power: continuous wave of 100 MHz and 500        W    -   Negative DC voltage applied to the lower electrode 18        -   Voltage value: −3000 V        -   Frequency: 200 kHz        -   Processing time: 60 seconds

In the first test experiment, an etching amount (film thicknessdecrement) of the silicon oxide film of the sample attached to thesurface of the ceiling plate 34 at the chamber 12 c side, an etchingamount (film thickness decrement) of the silicon oxide film of thesample attached to the sidewall of the chamber main body 12 and anetching amount (film thickness decrement) of the silicon oxide film ofthe sample placed on the electrostatic chuck 20 are measured. FIG. 12Ais a graph showing a relationship between the duty ratio and the etchingamount of the silicon oxide film of the sample attached to the surfaceof the ceiling plate 34 at the chamber 12 c side obtained in the firsttest experiment, and FIG. 12B is a graph showing a relationship betweenthe duty ratio and the etching amount of the silicon oxide film of thesample attached to the sidewall of the chamber main body 12 obtained inthe first test experiment. FIG. 13 is a graph showing a relationshipbetween the duty ratio and the etching amount of the silicon oxide filmof the sample placed on the electrostatic chuck 20 obtained in the firsttest experiment.

As depicted in FIG. 13, dependency of the etching amount of the siliconoxide film of the sample placed on the electrostatic chuck 20 upon theduty ratio is found to be small. Further, as shown in FIG. 12A and FIG.12B, when the duty ratio is equal to or less than 35%, the etchingamount of the silicon oxide film of the sample attached to the surfaceof the ceiling plate 34 at the chamber 12 c side and the etching amountof the silicon oxide film of the sample attached to the sidewall of thechamber main body 12 are found to be reduced considerably. Accordingly,it is found out through the first test experiment that the dependency ofthe etching rate of the substrate upon the duty ratio occupied, withineach cycle PDC, by the period during which the negative DC voltage isapplied to the lower electrode 18 is small. Further, it is also foundout that the etching rate of the chamber main body 12 is greatlyreduced, that is, the energy of the ions irradiated to the inner wall ofthe chamber main body 12 is reduced when the duty ratio is small,particularly, equal to or less than 35%. Moreover, from the graphs ofFIG. 12A and FIG. 12B, it is deemed that the energy of the ionsirradiated to the inner wall of the chamber main body 12 would beconsiderably reduced if the duty ratio is equal to or less than 40%.

Second Test Experiment

In the second test experiment, samples each having a silicon oxide filmare attached to the surface of the ceiling plate 34 at the chamber 12side and the sidewall of the chamber main body 12 and a sample having asilicon oxide film is placed on the electrostatic chuck 20 of the plasmaprocessing apparatus 10. Then, plasma processing is performed under thefollowing conditions.

<Conditions for Plasma Processing in Second Test Experiment>

-   -   Internal pressure of the chamber 12 c: 20 mTorr (2.66 Pa)    -   Flow rate of gases supplied into the chamber 12 c        -   C₄F₈ gas: 24 sccm        -   O₂ gas: 16 sccm        -   Ar gas: 150 sccm    -   First radio frequency power: continuous wave of 100 MHz and 500        W    -   Negative DC voltage applied to the lower electrode 18        -   Voltage value: −3000 V        -   Frequency: 200 kHz        -   Duty ratio: 35%    -   Processing time: 60 seconds

Further, in a comparative experiment, samples each having a siliconoxide film are attached to the surface of the ceiling plate 34 at thechamber 12 side and the sidewall of the chamber main body 12 and asample having a silicon oxide film is placed on the electrostatic chuck20 of the plasma processing apparatus 10. Then, plasma processing isperformed under the following conditions. A condition for the secondradio frequency power in the comparative experiment is set such that anetching amount (film thickness decrement) of the silicon oxide film ofthe sample placed on the electrostatic chuck 20 is substantially same inthe plasma processing of the second test experiment and the plasmaprocessing of the comparative experiment.

<Conditions for Plasma Processing in Comparative Experiment>

-   -   Internal pressure of the chamber 12 c: 20 mTorr (2.66 Pa)    -   Flow rate of gases supplied into the chamber 12 c        -   C₄F₈ gas: 24 sccm        -   O₂ gas: 16 sccm        -   Ar gas: 150 sccm    -   First radio frequency power: continuous wave of 100 MHz and 500        W    -   Second radio frequency power: continuous wave of 400 kHz and        2500 W    -   Processing time: 60 seconds

In each of the second test experiment and the comparative experiment, anetching amount (film thickness decrement) of the silicon oxide film ofthe sample attached to the surface of the ceiling plate 34 at thechamber 12 c side, and an etching amount (film thickness decrement) ofthe silicon oxide film of the sample attached to the sidewall of thechamber main body 12 are measured. FIG. 14A is a graph showing theetching amounts of the silicon oxide films of the samples attached onthe surface of the ceiling late 34 at the chamber 12 c side obtained inthe second test experiment and the comparative experiment, respectively,and FIG. 14B is a graph showing the etching amounts of the silicon oxidefilms of the samples attached on the sidewall of the chamber main body12 obtained in the second test experiment and the comparativeexperiment, respectively. On the graph of FIG. 14A, a horizontal axisrepresents a distance of a measurement position within the sampleattached to the surface of the ceiling plate 34 at the chamber 12 c sidefrom a center of the chamber 12 c in a radial direction, and a verticalaxis indicates the etching amount of the silicon oxide film of thesample attached to the surface of the ceiling plate 34 at the chamber 12c side. On the graph of FIG. 14B, a horizontal axis represents adistance of a measurement position within the sample attached to thesidewall of the chamber main body 12 from the surface of the ceilingplate 34 at the chamber 12 c side in a vertical direction, and avertical axis indicates the etching amount of the silicon oxide film ofthe sample attached to the sidewall of the chamber main body 12.

As can be seen from FIG. 14A and FIG. 14B, as compared to thecomparative experiment using the second radio frequency power, in thesecond test experiment in which the negative DC voltage is periodicallyapplied to the lower electrode 18, the etching amount of the siliconoxide film of the sample attached to the surface of the ceiling plate 34at the chamber 12 c side and the etching amount of the silicon oxidefilm of the sample attached to the sidewall of the chamber main body 12are found to be reduced considerably. Accordingly, it is found out thatthe energy of the ions irradiated to the wall surface of the chambermain body 12 and the wall surface of the upper electrode 30 can begreatly reduced while suppressing reduction of the energy of the ionsirradiated to the substrate on the electrostatic chuck 20 by applyingthe negative DC voltage to the lower electrode 18 periodically, ascompared to the case where the second radio frequency power, that is,the radio frequency bias power is used.

From the foregoing, it will be appreciated that various embodiments ofthe present disclosure have been described herein for purposes ofillustration, and that various modifications may be made withoutdeparting from the scope and spirit of the present disclosure.Accordingly, the various embodiments disclosed herein are not intendedto be limiting. The scope of the inventive concept is defined by thefollowing claims and their equivalents rather than by the detaileddescription of the exemplary embodiments. It shall be understood thatall modifications and embodiments conceived from the meaning and scopeof the claims and their equivalents are included in the scope of theinventive concept.

We claim:
 1. A plasma etching method performed in a plasma processingapparatus, wherein the plasma processing apparatus comprises: a chambermain body in which a chamber is provided; a stage, including a lowerelectrode, provided within the chamber main body and configured tosupport a substrate placed thereon; a radio frequency power supplyconfigured to supply a radio frequency power for exciting a gas suppliedinto the chamber; and one or more DC power supplies configured togenerate a negative DC voltage to be applied to the lower electrode,wherein the plasma etching method comprises: supplying the radiofrequency power from the radio frequency power supply to generate plasmaof the gas supplied into the chamber; and applying the negative DCvoltage to the lower electrode from the one or more DC power supplies toattract ions in the plasma onto the substrate, and wherein, in theapplying of the negative DC voltage, the negative DC voltage is appliedto the lower electrode periodically, and a duty ratio is set to be equalto or less than 40%, wherein the duty ratio is a percentage occupiedwithin a single cycle by a period during which the negative DC voltageis applied to the lower electrode.
 2. The plasma processing method ofclaim 1, wherein the duty ratio is set to be equal to or less than 35%.3. The plasma processing method of claim 1, wherein the plasmaprocessing apparatus comprises multiple DC power supplies, and thenegative DC voltage applied to the lower electrode within each cycle isgenerated by negative DC voltages outputted from the multiple DC powersupplies in sequence.
 4. The plasma processing method of claim 1,wherein the radio frequency power is supplied in the period during whichthe negative DC voltage is applied, and the supplying of the radiofrequency power is stopped in a period during which the applying of thenegative DC voltage is stopped.
 5. The plasma etching method of claim 1,further comprising: cleaning an inner wall of the chamber by setting theduty ratio to be larger than 40%.
 6. The A plasma processing methodperformed in a plasma processing apparatus, wherein the plasmaprocessing apparatus comprises: a chamber main body in which a chamberis provided; a stage, including a lower electrode, provided within thechamber main body and configured to support a substrate placed thereon;a radio frequency power supply configured to supply a radio frequencypower for exciting a gas supplied into the chamber; and one or more DCpower supplies configured to generate a negative DC voltage to beapplied to the lower electrode, wherein the plasma processing methodcomprises: supplying the radio frequency power from the radio frequencypower supply to generate plasma of the gas supplied into the chamber;and applying the negative DC voltage to the lower electrode from the oneor more DC power supplies to attract ions in the plasma onto thesubstrate, wherein, in the applying of the negative DC voltage, thenegative DC voltage is applied to the lower electrode periodically, anda duty ratio is set to be equal to or less than 40%, wherein the dutyratio is a percentage occupied within a single cycle by a period duringwhich the negative DC voltage is applied to the lower electrode, andwherein the supplying of the radio frequency power is stopped in theperiod during which the negative DC voltage is applied, and the radiofrequency power is supplied in a period during which the applying of thenegative DC voltage is stopped.
 7. A plasma etching apparatus,comprising: a chamber main body in which a chamber is provided; a stage,including a lower electrode, provided within the chamber main body andconfigured to support a substrate placed thereon; a radio frequencypower supply configured to supply a radio frequency power for exciting agas supplied into the chamber; one or more DC power supplies configuredto generate a negative DC voltage to be applied to the lower electrode;a switching unit configured to allow the application of the negative DCvoltage to the lower electrode to be stopped; and a controllerconfigured to control the switching unit, wherein the controllercontrols the switching unit such that the negative DC voltage from theone or more DC power supplies is applied to the lower electrodeperiodically to attract ions in plasma of a gas generated within thechamber onto the substrate and a plasma etching process is performed onthe substrate, and such that a duty ratio is set to be equal to or lessthan 40%, wherein the duty ratio is a percentage occupied within asingle cycle by a period during which the negative DC voltage is appliedto the lower electrode.
 8. The plasma processing apparatus of claim 7,wherein the controller controls the switching unit such that the dutyratio is set to be equal to or less than 35%.
 9. The plasma processingapparatus of claim 7, further comprising: multiple DC power supplies,and wherein the controller controls the switching unit such that thenegative DC voltage applied to the lower electrode within each of thecycles is generated by the negative DC voltages outputted from themultiple DC power supplies in sequence.
 10. The plasma processingapparatus of claim 7, wherein the controller controls the radiofrequency power supply such that the radio frequency power is suppliedin the period during which the negative DC voltage is applied, and thesupply of the radio frequency power is stopped in a period during whichthe application of the negative DC voltage is stopped.
 11. The plasmaprocessing apparatus of claim 7, wherein the controller controls theradio frequency power supply such that the supply of the radio frequencypower is stopped in the period during which the negative DC voltage isapplied, and the radio frequency power is supplied in a period duringwhich the application of the negative DC voltage is stopped.
 12. Theplasma etching apparatus of claim 7, wherein the controller is furtherconfigured to clean an inner wall of the chamber by setting the dutyratio to be larger than 40%.
 13. The plasma etching apparatus of claim7, wherein the plasma etching apparatus is a capacitively coupled plasmaprocessing apparatus.
 14. The plasma etching apparatus of claim 7,wherein the plasma etching apparatus is an inductively coupled plasmaprocessing apparatus.